Introduced species can be a serious problem anywhere, but especially on islands. Here is a definition of introduced species, and why they can be problematic.
I have lived in various parts of the USA, Madagascar, and now New Zealand. It seems like everywhere I’ve lived there were introduced species, some of which were a problem, and others were welcomed. Utah has myrtle spurge (problem) and Madagascar has lots of eucalyptus (welcomed by people). However, nowhere else was I so aware of native and introduced species as I am here in New Zealand. The introduced species in New Zealand, especially the mammals, are wiping out native birds, reptiles, and insects.
According to the World Conservation Union, alien species are the second greatest threat to biodiversity (after habitat loss).
What Is An Introduced Species?
An introduced species is simply a species that was brought to an area that it did not previously live. People may have brought it on purpose or it may have come accidentally (like ship rats in New Zealand).
It’s Impossible To Predict All Outcomes On Introducing Species
It’s almost impossible to know what will happen when a new species is introduced to an area that it had not previously lived. Despite lots of research and time there may always be unanticipated outcomes.
There is something called the law of unintended consequences. Basically, it states that it’s impossible to predict all outcomes and often there will be unintended outcomes.
Are Introduced Species Always Bad?
No, not really. There are many introduced species that are important for people. For example, some of the most common grain crops such as wheat, and rice are now grown all over the world.
Here in New Zealand we have millions upon millions of introduced mammals. Some are good for people, such as cattle and sheep, but others are serious problems, such as stoats and rats.
I say not really, because even though cattle may not be a direct threat to native wildlife, they are the cause of major habitat loss. Remember, NZ used to be a land of forest, but now it’s major land cover is introduced grassland (much of which is pasture land).
How Can Introduced Species Take Over And Become Widespread?
There are a few reasons that these introduced species can come to a new area and thrive. I will do my best to explain a few of the main ones here.
It evolved elsewhere – species that evolved over millions of years grew into a state of balance to keep their populations in check (known as co-evolution). A good example is the cheetah and antelope. They evolved together as faster antelopes survived more, and then faster cheetah caught more antelope. The prey evolved ways to survive and protect itself and the predators evolved ways to catch the prey.
However, when you bring a new species to an area where it has not lived it does not fit smoothly into the natural ecosystem. There are no predators to keep it in check and it’s prey is not adapted to give it a good chance at survival.
For example, many native birds in New Zealand evolved to be flightless due to a lack of ground predators. Then when rats and stoats were introduced they found those flightless birds easy prey. Most likely the birds would not have evolved to be flightless if the rats had been in New Zealand the entire time.
Fill vacant niche – a species may come to a new area and find a niche or place in the ecosystem that is vacant. It would then be able to quickly fill that missing void and thrive.
Outcompete native species – an introduced species may move into an area and be able to outcompete native species for a resource. This would cause the native species to diminish. For example, in New Zealand introduced german wasps thrive in the beech forests of the south island. They eat up to 90% of the honey dew produced by scale insects. This deprives the native birds, bats, insects, and lizards of this food source.